A study of parameters to optimise the design of LPE dipping apparatus

The theoretical treatment of LPE growth of magnetic garnet materials by horizontal spinning has given good agreement between predicted and observed growth rates. However, for practical purposes it is necessary to obtain basic data for the solutions used; these include: the liquidus temperature, density, viscosity, diffusion coefficients, heat of crystallisation, and the variation (where appropriate) of these parameters with temperature and melt composition. Studies have been made on selected compositions in the system: PbO−B 2 O 3 −Y 2 O 3 −Eu 2 O 3 −Ga 2 O 3 −Fe 2 O 3 , and the results obtained are presented. The data acquired have been used to interpret the experimental results for LPE growth of magnetic garnet on GGG substrates. It is shown that good reproducibility is achievable provided attention is given in particular to the selection of suitable substrate rotation rates and values of undercooling. Consideration is also given to the effective segregation coefficients for the various constituents. The heat of crystallisation measured indicates that constituents may be present as separate oxide constituents in the melt, presumably as complexes with solvent constituents. The significance of this fact is used to explain in a qualitative manner the observed effective segregation coefficients. From the measured data and theoretical principles based on the Burton, Prim and Slichter model of a rotating disc, the practical requirements for growth equipment, suitable for laboratory scale controlled growth of garnet epilayers, are described. Practical details are given of the techniques used in the investigations described. The general approach of this work, concerned as it is with establishing the necessary preliminary data, should be particularly useful for studies on new solvent-solute systems.